Bacteria protect their genomes from being the target of bacterial restriction enzymes. This is accomplished by adding a special chemical moiety called a “methyl group” to the bacterial genome as a molecular “repellant” against bacterial restriction enzyme actions. (This is an elegant solution, to be sure.) DNA methylation is widely acknowledged as playing a pivotal role in cancer biogenesis.
CRISPR was defined as “clustered / regularly / interspaced / palindromic / repeats.” Each acronym component is significant. Four adjectives related to the central word, “repeats,” are described below.
Palindrome in English is defined as a sequence of letters that can be read either forward or backward, and the same sequence of words remains. Classic palindromic word examples in the English vocabulary include “kayak” and “civic.” Both words can be read left to right or vice versa, and the same word with the same meaning is retained. The spelling remains the same reading, from left to right or vice versa.
The palindromic sequences in CRISPR are, on average, 30 DNA bases in length that follow the complementary base pairing of A—T and G—C. Furthermore, CRISPR palindrome sequences are characterized by five features.
The palindrome (feature #1) occurs frequently as:
- Repeats (feature #2), which serve as molecular hedges
- Containing interspacers (feature #3), the actual DNA sequences that the bacterium has obtained from invading phages
- Repeats occur regularly (feature #4) and appear as clusters (feature #5)
